o-Chloromethyl-substituted benzoyl chlorides are important intermediates for preparing, for example, pesticidally active compounds as described in the patents EP-A 460 575, EP-A 463 488, WO-A 95/18789, WO-A 95/21154 and WO-A 97/15552.
o-Chloromethyl-substituted benzoyl chlorides can be prepared, for example, by reacting benzo-fused lactones with thionyl chloride or phosgene. If thionyl chloride is used, the apparatus is simplified and the safety precautions reduced.
EP-A 676 389 describes the preparation of o-chloromethylbenzoyl chlorides from benzo-fused lactones using thionyl chloride in the presence of a nitrogen compound. To achieve a satisfactory conversion, reaction temperatures of 160–170° C. are required, at which thionyl chloride is already partially decomposed, resulting in the formation of troublesome byproducts. Furthermore, the addition of gaseous hydrochloric acid is required. Finally, in some cases the yields are considerably less than 90%.
WO 97/12854 describes a process for preparing o-chloromethylbenzoyl chlorides by phosgenation of benzo-fused lactones in the presence of a triarylphosphine oxide catalyst at 170° C. In contrast to thionyl chloride, phosgene is thermally stable under these conditions; however, the handling of phosgene and its holdup in the condenser at the high temperatures involved are made more difficult by increased safety precautions. Furthermore, under these conditions the reaction product is under high thermal stress, which may result in its partial decomposition.
In WO-A 99/16743, the reaction with thionyl chloride is carried out in the presence of a quaternary ammonium salt and a Lewis acid at 90–100° C. However, quaternary ammonium salts are problematic from an environmental point of view and have the following technical disadvantages: sublimation may result in parts of the plant being blocked. Furthermore, the salts are hygroscopic, which may lead to water being introduced, resulting in more chlorinating agent being consumed. Finally, the ammonium salts interfere with the distillative purification of the o-chloromethylbenzoyl chlorides.